ABSTRACT The Cardiac Imaging Core (Core B) will provide service to all 3 projects with the goals of generating confocal microscopy- and in vivo ultrasound ? based analyses of cardiac development, structure, and function. Core B will be directed by Michael Rubart, M.D., who will provide expertise in confocal imaging of tissues. Dr. Rubart will be assisted by Ronald Payne, M.D., who will provide expertise in ultrasound imaging of embryonic and postnatal cardiac development and function. Core B's services enhance the efficiency of the Projects by providing consistent expertise in the capture and evaluation of images from tissue sections and hearts in vivo, using confocal microscopy and echocardiography, respectively. There are 2 Specific Aims for the Core: Aim 1 will provide high-quality, unbiased confocal fluorescence imaging of the pre- and postnatal heart, as well as quantitative image analyses. Approaches utilized in Aim 1 will quantitatively assess (i) primitive streak formation and node polarity (Project 1), (ii) sarcomeric organization and cardiomyocyte polarity (Project 1-3), and (iii) ventricular wall trabeculation and compaction (Project 3). Imaging will be performed using a laser scanning confocal microscope equipped with multiple laser excitation lines and detector channels, as well as a variety of high/low magnification, high/low numerical aperture objectives. Aim 2 will provide high-resolution in vivo ultrasound imaging of the pre- and postnatal heart in Projects 1-3 in order to generate quantitative data of structure, function, and flow relative to genetic alterations in cardiac development. In addition, ultrasound imaging will allow the study of longitudinal structural and functional data. Ultrasound imaging will utilize probes with frequency bands from 13 to 70 MHz, and linear array transducer technology, enabling imaging of hearts at different stages of development and frame acquisition at high rates, respectively. Available analysis software will enable quantification of cardiac contractile performance, chamber dimensions, and flow pattern, including detection and size estimation of intracardiac shunts. Overall, technologies utilized in the Cardiac Imaging Core will enable unbiased, quantitative assessments of changes in cardiac structure and function as a result of genetic alterations studied in each of the three Projects of this application.